Chains are known which are currently made by hand starting from open links, that is, links having and oval helix-like profile and a pitch is approximately equal to twice the thickness of the wire from which they are made. Each link being fir linked by the insertion and rotation of an open link with respect to the link last linked. The open link is then closed and finally twisted to achieve the shape of an eight.
Obviously, the manual formation of such chains calls for a great deal of time, great care and accuracy by the operator. The manufacturing costs therefore cause the production to be restricted to chains of precious metal such as gold, silver and other less noble metals.
The present invention has the object to eliminate the above mentioned drawbacks by providing a method and a machine for mechanically and automatically making chains with figure eight-shaped links so as to increase the accuracy, rate and reliability of production and, thereby, drastically reducing the manufacturing costs.
This object has been achieved, according to the invention, by implementing a method which comprises, in sequence, the following steps:
holding, in a predetermined joining position, the link of the chain which has been last linked; an separately:
gripping a loose and open link from a machine forming of oval helix-shaped links;
positioning said loose and open link into a plane substantially orthogonal to the one of the blocked link of the chain;
introducing the two arms of said loose and open link into the corresponding eyes of the held link and rotating the latter about its own axis to achieve the joining;
leaving the held link of the chain;
closing the spread apart ends of the loose link so joined and twisting it to form an eight.
According to a preferred embodiment, a machine for the automatic formation of chains with figure eight-shaped links according to the said method, comprises:
means for positioning the last link of the chain, in the course of formation, to allow for the passive joining of a corresponding loose and open link;
means for moving each loose and open link made from a wire bent in the form of an oval helix by a "screw-nut machine[ transfer of the same link to a position for the active joining thereof with the corresponding last link of the chain and, subsequently, moving the last link to a successive position for the closing and twisting thereof;
means for closing each loose and open link after the joining thereof and for performing the figure eight-shape twist thereof.
The advantages attained by the present invention consist essentially in that it is possible to mechanically and automatically form chains with figure eight-shaped links; it is possible to drastically reduce the production times and, therefore, the relevant costs and that it is possible to increase the uniformity and reliability of the finished product, yet maintaining a versatility as far as the geometrical dimensions and the nature of the material of the links are concerned.
These and further advantages and characteristics of the invention will be more and better understood by any skilled in the art from the following description in conjunction with the attached drawings given as a practical exemplification of the invention, but not to be considered in a limiting sense; wherein: